Novel insights into structure and function of MRP8 (S100A8) and MRP14 (S100A9)

The two migration inhibitory factor- (MIF)-related protein-8 (MRP8; S100A8X ) and MRP14 (S100A9) are two calcium-binding proteins of the S100 family. T hese proteins are expressed during myeloid differentiation, are abundant in granulocytes and monocytes, and form a heterodimeric complex in a Ca2+-dep endent manner. Phagocytes expressing MRP8 and MRP14 belong to the early inf iltrating cells and dominate acute inflammatory lesions. In addition, eleva ted serum levels of MRP8 and MRP14 have been found in patients suffering fr om a number of inflammatory disorders including cystic fibrosis, rheumatoid arthritis, and chronic bronchitis, suggesting conceivable extracellular ro les for these proteins. Although a number of possible functions for MRP8/14 have been proposed, the biological function still remains unclear. This re view addresses recent developments regarding the MRP14-mediated promotion o f leukocyte-endothelial cell-interactions and the characterization of MRP8/ 14 heterodimers as a fatty acid binding protein complex. In view of the cur rent knowledge, the authors will hypothesize that MRP8 and MRP14 play an im portant role in leukocyte trafficking, but do not affect neutrophil effecto r functions. (C) 1998 Elsevier Science B.V. All rights reserved.